Various ways of adding passwords
1 look at Disk ID
2 look at registry
3 ping a web server
4 check a web site for date no wind clock back
5 look for a file
Most important compile your lisp to a fas file.
I would suggest using an AutoLISP application to perform the required operations, and using the Script purely to open each drawing, evaluate the AutoLISP program, and then save & close the drawing - I describe this technique here.